The present invention relates to a modulator for antiskid brake system for adjusting brake fluid pressure during antiskid brake control in a vehicle.
Generally, in an antiskid brake system to be installed on a vehicle, a flow regulating valve 6 is mounted upstream of a passage selector valve 5 and the passage selector valve 5 is furnished on a supply passage 4, which communicates master cylinder 1 with brake cylinder 3 of wheel. The passage selector valve 5 and flow regulating valve 6 are also furnished on the supply passage to the brake cylinder of the other wheels.
In normal brake operation, there occurs almost no pressure difference between the portion upstream of the flow regulating valve 6 and downstream of the passage selector valve 5, and the flow regulating valve 6 is maintained as shown in the FIG. 5. Under this condition, the brake fluid from the master cylinder 1 is supplied to the brake cylinder 3 through a first passage 7, and the flow of the brake fluid is not restricted by the orifice 9 of the second passage 8. Therefore, the brake fluid pressure in the brake cylinder 3 is rapidly increased when brake pedal is depressed.
When electronic controller (not shown) detects that the wheel 2 is in skid state, the passage selector valve 5 is switched on. As a result, the brake fluid in the brake cylinder 3 passes through a pressure reducing passage 10 and is discharged to a sump unit 11, and the fluid pressure in the brake cylinder 3 is decreased. For this reason, a pressure difference is generated between the supply passage 4 upstream of the flow regulating valve 6 and the supply passage 4 downstream of the passage selector valve 5. When this pressure difference exceeds the predetermined value, the first passage 7 of the flow regulating valve 6 is closed. As the result, a flow regulating valve 6 is communicated only through the second passage 8 having an orifice 9.
When it is detected that the wheel is in skid state, the electronic controller drives the pump 12. Accordingly, the pump 12 sends the brake fluid in the sump unit 11 into the volume chamber 13 to accumulate the predetermined fluid pressure in the volume chamber 13.
When the electronic controller detects under this condition that the wheel has been released from the skid state, the passage selector valve 5 is switched off, and the brake cylinder 3 and the master cylinder 1 are communicated with each other through the second passage 8. As the result, the brake fluid, which has been returned to the supply passage 4 upstream of the flow regulating valve 6, is sent to the brake cylinder 3 through the second passage 8 of the flow regulating valve 6. In this case, the flow rate of the brake fluid is restricted by the orifice 9 of the second passage 8, and the fluid pressure in the brake cylinder 3 is gradually increased.
The modulator 14 of the antiskid brake system in this embodiment comprises a passage selector valve 5, a flow regulating valve 6, a sump unit 11, a pump 12 and a volume chamber 13.
Through the control of the passage selector valve 5, flow regulating valve 6 and pump 12 in the modulator 14 by the electronic controller, the antiskid brake control for the wheel 2 is performed.
As shown in FIG. 6, the conventional type flow regulating valve 6 of the modulator 14 is provided with an opening valve 15 in the first passage 7 and an orifice unit 9 on the second passage 8. The opening valve 15 is further furnished with a plunger 15a on both ends of which the pressure upstream of the opening valve 15 and the pressure downstream of the passage selector valve 5 are applied. When the pressure difference is lower than the predetermined value, the opening valve 15 is pushed by a spring 16 and maintains the first passage 7 in open state as shown in the figure. When the pressure difference exceeds the predetermined value, the opening valve 15 closes the first passage 7. Thus, the sections upstream and downstream of the flow regulating valve 6 are communicated with each other through the second passage 8 having the orifice 9.
However, in such flow regulating valve 6, the opening valve 15 may also close the first passage 7 when in normal brake operation other than the antiskid brake control if the above pressure difference exceeds the preset value. When the first passage 7 is closed, the braking operation is slowed by the action of the orifice 9 which is a problem if a quick braking operation is needed.
For this reason, it is proposed that the opening valve 15 is operated by the difference between the discharge pressure of the pump 12 operating only during antiskid brake control and the pressure downstream of the passage selector valve 5, so that the first passage 7 is closed only during the antiskid brake control. In so doing, slow braking operation can be avoided during emergency braking. In this case, the opening valve 15 is designed in spool type.
However, in such simple arrangement, it is necessary to provide a passage to lead the pilot pressure to this spool in order to operate it. This results in a complicated arrangement of passages in the modulator. As the result, there arise many problems such as the difficulties in producing such valves, providing holes in passages, modulator, etc.
Also, to meet the requirements for such arrangement, a large size modulator is required. Moreover, difficult production and large size modulator mean higher manufacturing cost.